The invention relates to compositions and methods for the production and modification of oil bodies in various host cell types. The invention relates to methods for the production of photosynthetic cells and plants with increased CO2 assimilation rates and methods for the production of oil from plants.
In nature, flowering plants efficiently store energy in their seeds through the accumulation of oil, namely triacylglycerol (TAG) and store it in discreet oil bodies by embedding a phospholipid protein monolayer around the oil body. These seed crops have been used in a variety of agricultural applications as feed and more recently also as a feedstock source for biofuels. On a per weight basis, lipids have approximately double the energy content of either proteins or carbohydrates and as such, substantial focus has been placed on raising the oil content of various species, most notably plants. Beyond the energy aspect, the oil bodies themselves also have unique properties and form the basis for a number of biotechnical applications including but not limited to the purification of recombinant proteins, formation of multimeric protein complexes, emulsification and the delivery of bio-actives.
Unfortunately plant seeds represent a very small percentage of total plant biomass and with the demand for improved agricultural productivity and alternative energies it is recognised that current oil production from a number of devoted seed crops is insufficient. Research efforts have focused on not only increasing the productivity of oil production within plant seeds but also oil production in other cell types and species.
Traditional breeding and mutagenesis have offered incremental successes in this area; however genetic engineering has made the furthest strides in modifying organisms to produce elevated oil levels. While certain groups have worked along various parts of the oil synthesis pathway to up-regulate oil production within the seed, others groups have focused on increasing oil in cell types that represent a larger portion of the biomass.
While genetic engineering has made some progress in increasing oil content in certain targets, significant challenges still remain. Further productivity increases can still be realized in oil body production in the seed and the means to produce oil bodies similar to those of a plant seed in other cell types and species has yet to be achieved.
The increasing global population presents demand for higher yielding crops with enhanced production (photosynthetic carbon assimilation).
Ribulose biphosphate carboxlase (Rubisco) is the key enzyme responsible for photosynthetic carbon assimilation. In the presence of O2, Rubisco also performs an oxygenase reaction which initiates the photorespiratory cycle which results in an indirect loss of fixed nitrogen and CO2 from the cell which need to be recovered. Genetic modification to increase the specificity of Rubisco for CO2 relative to O2 and to increase the catalytic rate of Rubisco in crop plants would be of great agronomic value. Parry et al, (2003) reviewed the progress to date, concluding that there are still many technical barriers to overcome and to date all engineering attempts have thus far failed to produce a better Rubisco (Peterhansel et al. 2008).
In nature, a number of higher plants (C4 plants) have evolved energy requiring mechanisms to increase the concentration of intracellular CO2 in close proximity to Rubisco thereby increasing the proportion of carboxylase reactions. Maize for example has achieved this by a manipulation of the plant's architecture enabling a different initial process of fixing CO2, known as C4 metabolism. The agronomic downside of this evolved modification is an increase in leaf fibre resulting in a comparatively poor digestibility of leaves from C4 plants. C4 photosynthesis is thought to be a product of convergent evolution having developed on separate occasions in very different taxa. However, this adaptation is only possible for multi-cellular organisms (and not for photosynthetic unicellular organisms such as algae). Algae have a variety of different mechanisms to concentrate CO2; however, there appears to be a continuum in the degree to which the CO2 concentration mechanism (CCM) is expressed in response to external dissolved inorganic carbon (DIC) concentration, with higher concentrations leading to a greater degree of suppression of CCM activity. Two reviews have covered the CCMs in algae as well as their modulation and mechanisms and are incorporated herein by reference (Giordano, Beardall et al. 2005; Moroney and Ynalvez 2007). The vascular plants that currently constituted the largest percentage of the human staple diet are C3 (rice and tubers) and not C4 plants. Similarly, many oil seed crops (canola, sunflower, safflower) and many meat and dairy animal feed crops (legumes, cereals, soy, forage grasses) are C3 plants.
Increasing the efficiency of CO2 assimilation, should therefore concurrently increase abiotic stress tolerance and nitrogen use efficiency and would be of significant agronomical benefit for C3 plants and photosynthetic microorganisms.
Therefore, mechanisms for elevating CO2 concentration in the chloroplast, reducing photorespiration and subsequently increasing abiotic stress tolerance and productivity would be of significant agronomical benefit for C3 plants and photosynthetic microorganisms.
It is an object of the invention to provide methods for increasing the rate of CO2 assimilation in photosynthetic cells and plants, and methods for producing photosynthetic cells and plants with an increased rate of CO2 assimilation.
In nature, flowering plants efficiently store energy in their seeds through the accumulation of oil, namely triacylglycerol (TAG) and store it in discreet oil bodies by embedding a phospholipid protein monolayer around the oil body. These seed crops have been used in a variety of agricultural applications as feed and more recently also as a feedstock source for biofuels. On a per weight basis, lipids have approximately double the energy content of either proteins or carbohydrates and as such, substantial focus has been placed on raising the oil content of various species, most notably plants.
Unfortunately plant seeds represent a very small percentage of total plant biomass and with the demand for improved agricultural productivity and alternative energies it is recognised that current oil production from a number of devoted seed crops is insufficient. Research efforts have focused on not only increasing the productivity of oil production within plant seeds but also oil production in other cell types and species.
Traditional breeding and mutagenesis have offered incremental successes in this area; however genetic engineering has made the furthest strides in modifying organisms to produce elevated oil levels. While certain groups have worked along various parts of the oil synthesis pathway to up-regulate oil production within the seed, others groups have focused on increasing oil in cell types that represent a larger portion of the biomass.
It is therefore a further object of the invention to provide methods for increasing the level of oil production in plant tissues/organs and/or methods for increasing the production of oil from plants.